How was the presumed age of the Universe determined?

1 Answer
Apr 23, 2018

Answer:

Using Hubble's law.

Explanation:

Hubble's law states that the further away a galaxy is, the faster it is moving:

#v prop d#

Because of this law, if it is extrapolated backward, it is implied that everything in the universe was once concentrated at one point- supporting the idea of the big bang and also makes it possible to estimate how long ago it was when everything was in one place- i.e the birth of the universe.

However, this is not using SI units, but rather the units for velocity is #kms^-1# and distance is measured in Mega-parsecs #MPc#.

This equation, being linear must have a constant- Hubble's constant:

#H_o#

Making the equation:

#v=H_od#

The value of the constant varies throughout the universe but on a VERY rough estimate we can say that the value of the constant is :

#H_o=70 kms^-1 MPc^-1#

This constant allows us to estimate the age of the universe using the equation:

#1/H_o approx T#

However, the Hubble constant must be transferred into SI units for this to work...

So let's find the value of the constant:
#70 kms^-1=70 000 ms^-1#

1 parsec= 3.26 ly= #3.08 times 10^16 m#

1 Mega-parsec(1 million parsecs)=#(3.08 times 10^16 times 10^6m)#

#H_o=70 kms^-1 MPc^-1=(70 times 10^3)/(10^6 times 3.08 times 10^16)= 2.27 times 10^-18#

Inverse it to find Hubble time:

#1/(2.27 times 10^-18) approx T#

#T approx 4.4 times 10^17 s#

#T approx 1.4 times 10^10# years

Which is almost 14 billion years, but scientists often say that the value is 13.8 with an uncertainty of #+-0.2# billion years, so we are within the acceptable range.

And that is basically how the age of the universe can be estimated.